This invention relates generally to the field of animal nutrition and more particularly to feedstuffs of substantially increased crude protein content for ruminant animals. Still more specifically, the invention relates to improving the ruminant nutritional value of poor quality plant materials having a relatively low crude protein content.
As is known, the ruminant animal has the ability to convert poor quality roughages and nonprotein nitrogen into high quality protein. This conversion is accomplished by bacteria present in the rumen. The ruminant is not highly efficient, however, in transforming forages into ruminant products such as meat and milk. One major factor that limits this efficiency is the level of nitrogen in the diet. Forages containing a low level of crude protein are not as valuable for the ruminant as are forages containing higher levels. For this reason, urea and other nonprotein nitrogen compounds have been used to boost the crude protein content of roughages containing low levels of nitrogen. One problem that frequently accompanies the feeding of high levels of nonprotein nitrogen compounds is the rapid hydrolysis of these compounds to NH.sub.3 by rumen bacterial enzymes. Urea, for example, is hydrolyzed by the enzyme urease into NH.sub.3 and CO.sub.2 in the rumen. Ammonia nitrogen is converted by rumen bacteria into amino acid nitrogen and then into bacterial protein. Ammonia present in excess of the level that bacteria can effectively use for protein synthesis is of little value to the ruminant, and the excess NH.sub.3 can cross the rumen wall, enter the blood stream and lead to NH.sub.3 toxicity. For this reason, it is desirable to retard the rate of hydrolysis of nonprotein nitrogen, so that excess and potentially toxic levels of NH.sub.3 are not produced in the rumen.
Numerous studies have been conducted in which crop residues or agricultural products were treated with NH.sub.3 for the purpose of increasing the crude protein content and/or digestibility of the roughage. In the rumen, the NH.sub.3 contained in nonprotein nitrogen compounds can be used by microbes for protein synthesis just as NH.sub.3 produced from urea or protein degradation can be used for this function.
Millar (Ind. Eng. Chem., 33:274, 1941) obtained a product containing four percent nitrogen when dry sugar beet pulp was ammoniated. McCall and Graham (J. Anim. Sci., 11:270, 1952) found that steers fed ammoniated furfural made higher daily gains than those fed urea as a protein supplement. Magruder et al. (J. Agr. Food Chem., 1:944, 1953) fed ammoniated hemicellulose extract to dairy heifers and found that animals used the nitrogen of this ration as well as they used the nitrogen of control rations containing soybean meal. Ammoniated molasses has been studied extensively as a crude protein source for ruminants. Wiggins (Sugar J., 18:18, 1956) found that imidazole and pyrazine derivatives in ammoniated molasses were responsible for the toxicity observed when this product was fed to animals. He also found that acidification of the product would prevent toxicity. Temple and Wiggins (Intern. Sugar J., 58:9, 1956) determined that as much as two percent nitrogen was absorbed by bagasse when anhydrous NH.sub.3 was added to it. The authors suggested that NH.sub.3 reacted with lignin and sugars in the bagasse. Reaction of NH.sub.3 with the sugars produced pyrazine and imidazole compounds, but the product was nontoxic for cattle.
Rice hulls and straw have been the poor quality plant materials most often used in ammoniation studies, probably because these materials are very low in crude protein. Eng (Feedstuffs, 36:44, 1964) found that ammoniated rice hulls improved the digestibility of low energy diets, but Furr and Carpenter (J. Anim. Sci., 26:919, 1967) showed that nitrogen digestibility of high energy diets was not improved when ammoniated rice hulls were fed at levels less than 10 percent of the total diet. Eng and Riewe (J. Anim. Sci., 22:736, 1963) have shown that ammoniated rice hulls are less toxic than urea to sheep. Waiss et al. (J. Anim. Sci., 35:109, 1972) treated several straws with aqueous NH.sub.3 for 30 days at ambient temperatures. They increased the enzymatic digestibility of the straws by 10 percent, and increased the nitrogen content by 133 percent. In another report, Garrett et al. (Proc. Western Section, Am. Soc. Anim. Sci., 25:317, 1974) determined that inclusion of ammoniated rice straw in lamb diets resulted in improved feed consumption and increased digestibility of dietary cellulose. In a review article by Hart et al. (Feedstuffs, 47:22, 1975), methods used to ammoniate rice straw, and to treat this material with alkali, have been described. These authors concluded that a process of low moisture alkali treatment of straw, followed by compaction, gives good digestibilities and has a number of advantages over other treatment processes.
In earlier work, Johanning (M. S. Thesis, University of Missouri, Columbia, 1976) treated corn stover with sodium hypochlorite, followed by aqueous NH.sub.3 in an effort to increase both the digestibility and crude protein level of the stover. This hypochlorite treatment oxidized the stover and increased its reactivity with NH.sub.3. Corn stover treated with hypochlorite plus aqueous NH.sub.3 contained approximately 20 percent crude protein, whereas stover treated with NH.sub.3 alone, without previous hypochlorite treatment, contained only about eight percent crude protein. Oxidation and ammoniation also improved in vitro dry matter digestibility of the corn stover in some instances.
The literature thus reveals that much effort has been directed toward increasing the efficiency of use of poor quality roughages and nonprotein nitrogen by ruminants. A limited success has been achieved by treating such feedstuffs with ammonia. A continuing need exists, therefore, for improving the crude protein level of poor quality plant materials through chemical treatment.